feat: sync with upstream — v1.2.0, in-app updates, Projects, modules

Brings the public tree back in line with the development repo after several
weeks of drift caused by a stale publish include list.

New:
- In-app update path: GET /update/check compares the checkout against
  origin/main and POST /update/apply runs `ncp upgrade` detached (pull,
  rebuild, restart). The sidebar shows the version, checks on click, and
  offers an "update available" pill.
- Projects: a project workspace groups chats and RAG documents, with
  per-project instructions and document retrieval scoped to the active
  project. Replaces the standalone Documents page.
- modules/: auto-discovered feature plugins (mail, network) with their
  frontend counterparts and tests.
- Memory curation runs in-process (synapse/memory/curator.py) on the chat
  model when a conversation goes idle. The separate memory service on :8001
  is gone, along with the launcher lines that started it.

Also: the KDE theme, panel and Promethean terminal assets, the full test
suite, and VERSION 1.2.0.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

assets/themes/KDE/look-and-feel/com.nexusos.desktop/contents/defaults

@@ -0,0 +1,25 @@
+[kdeglobals][KDE]
+widgetStyle=kvantum-dark
+
+[kdeglobals][General]
+ColorScheme=NexusOS
+
+[kdeglobals][Icons]
+Theme=NexusOS
+
+[plasmarc][Theme]
+name=NexusOS
+
+[Wallpaper]
+Image=NexusOS
+
+[kwinrc][org.kde.kdecoration2]
+library=org.kde.kwin.aurorae
+theme=__aurorae__svg__NexusOS
+
+[kscreenlockerrc][Greeter]
+Theme=org.kde.breeze.desktop
+
+[KSplash]
+Theme=com.nexusos.desktop
+Engine=KSplashQML